Influence of mask surface roughness on 22nm node extreme ultraviolet lithography

Abstract

Extreme Ultraviolet Lithography (EUVL) is one of the patterning technologies for the 22 nm node and below. Generally, EUVL used a reflectivity type mask consist of absorber layer on a mask blank substrate coated with Mo/Si multilayer. Especially, reflectivity from EUV mask multilayer could be one of the important factors to make EUV process to be ready for 22 nm node. In spite of the developed technologies, the reported experimental reflectivity (60-66 %) is much less than the theoretical reflectivity (73 %) from the perfect EUV mask multilayer because of the Mo/Si rough boundaries and multilayer top surface roughness. The surface roughness that occurs in deposition of multilayer makes the reflectivity loss. It seems that it might be difficult to reach the ideal reflectivity and 22 nm node process has to live up with the imperfect reflectivity. In this study, we focused on the influence of the surface roughness on the Mo/Si multilayer for 22 nm node. First we studied the reflectivity loss for the multilayer surface roughness. The magnitudes of short, medium, and long range roughness are compared in terms of the amplitude and phase non-uniformity because even 1 nm roughness can make huge difference in EUV. The aerial image and process latitude with surface roughness are studied and the possibility of 22 nm node patterning with surface roughness will be reported. © 2010 Copyright SPIE - The International Society for Optical Engineering.